New SiO masers associated with bright southern IRAS sources.

The discovery of 31 new SiO v = 1, J = 1 - 0 (43.122 GHz) masers associated with southern IRAS sources is reported. The candidate list for the search was produced systematically, and the high detection success rate (about 50 percent) led to the consideration of differences between stars associated with masers and those showing maser emission. A set of conditions is proposed which virtually guarantee the presence of detectable stellar SiO maser. One of the most important requirements is large optical variability (2.5 mag or greater), a condition associated with high mass-loss rate. In addition, it is found that the maser-to-infrared flux ratio is approximately proportional to the mass-loss rate. New polarization observations of the SiO maser associated with R Aqr, one of the two symbiotic stars known to show any type of maser emission, are also presented.